What data is being collected
The extension uses Google Analytics to track its installs and usage. A single pageview is tracked every time the extension's background script is executed. That means one pageview for each browser session (the whole time the browser is running), regardless of the amount of scrobbled songs or supported websites visited.
The extension does not track visits of any particular pages. It also does not access your personal data on any of supported websites. Nor does it interfere with any page's contents.
How the data is being used
The data collected by Google Analytics is used to track usage of the extension in time and across various browsers and their versions. The data can be used for strategic decisions regarding the extension's development and marketing.